The present invention relates to the art of musical instruments, and more particularly relates to pickups and sustainers for use with musical instruments having vibratory elements such as strings.
Many conventional musical instruments utilize strings or other vibratory elements to produce sound. In the traditional versions of such instruments, the vibration of the string or other element is directly converted into sound, through acoustic coupling between the vibratory element and the air. Typically, the body of the conventional instrument has significant acoustic response and aids in conversion of the vibration to sound. In the so-called "electric" versions of such instruments, the vibration of the element is converted to electrical signals by transducers, commonly referred to as "pickups", and these electrical signals are amplified and reproduced by loudspeakers. Several pickups may be provided, and the electrical signals may be derived from any one of these pickups or from a blend of signals from more than one pickup. For example, in a stringed musical instrument, the various pickups may be disposed at spaced apart locations along the length of the string to detect the different motions of different sections of the string.
Electromagnetic pickups are commonly employed for this purpose. Each electromagnetic pickup typically includes a permanent magnet and at least one coil. The coil and permanent magnet are mounted to the instrument body in proximity to ferromagnetic strings of the instrument so that flux from the magnet is linked to the coil via a magnetic path including the strings. As the strings vibrate, they alter the magnetic reluctance of the path and hence alter the amount of flux passing through the coil, so that signal voltages are induced in the coil responsive to the vibration.
Pickups utilized heretofore have been designed to maximize the signal voltage. Such pickup coils typically include thousands of turns and have very high inductance, ordinarily about 2.5-10 Henries. These coils, and the pickups incorporating the same are expensive. The problem is particularly severe in the case of an instrument incorporating plural pickups.
Devices referred to as sustainers have also been employed heretofore in conjunction with electric musical instruments such as electric guitars. The sustainer normally incorporates an electromagnetic transducer referred to as a "driver" for applying forces to the vibratory element of the instrument in response to an electrical signal. The sustainer also includes a feedback circuit for accepting a signal representing motion of the string, such as a signal from a pickup, and transmitting the feedback signal to the driver, typically with substantial amplification. Thus, the forces applied by the driver tend to reinforce the motion of the vibratory element or string and hence to sustain its vibration. The aforementioned patents and patent applications disclose particularly useful designs for such sustainers. The sustainers are arranged to compensate for phase shifts in the driver and/or pickup and thus assure that the driving forces applied by the driver to the string or other vibratory element are substantially in phase with the vibration. This provides a particularly effective sustain action.
A driver typically is designed according to criteria different from those employees in design of a pickup. A driver ordinarily is a low impedance devices with a coil having a relatively small number of turns and a relatively low inductance, typically about 3 milliHenries. These devices may include a core of magnetically "soft" material, i.e., a material of high magnetic permeability such as iron. These characteristics provide high efficiency in conversion of the electrical feedback signal to force applied to the strings. Typically, the driver is provided in addition to all of the pickups incorporated in the instruments, thus further adding to the cost of the instrument. The driver may be positioned on the instrument at a location which would otherwise be occupied by a pickup. This makes it impractical to provide a pickup at that location.
Sustainers have been provided heretofore with phase inversion devices, or with selectable diodes in the feedback circuit for selectively inverting the feedback signal. This reverses the phase relationship between the drive force applied by the driver and the vibration of the string. See U.S. Pat. Nos. 3,813,473; Reissue 25,728; 4,245,540. Use of the feedback signal without phase inversion tends to reinforce the fundamental mode vibration of a string, whereas use of the feedback signal with phase inversion tends to reinforce harmonics in vibration of the string. The selectively operable phase inversion device allows the musician to choose either effect. However, the frequency and phase response of the feedback circuit (apart from the inversion) is the same. This represents a compromise at best. The optimum response for driving the fundamental is different from the optimum frequency response for driving the harmonics.
Accordingly, there have been substantial, unmet needs for further improvements in musical instruments, and particularly in pickup systems, sustainers and musical instruments incorporating these elements.